What does the air we normally breathe consist primarily of?

The air we normally breathe consists primarily of nitrogen and oxygen. In the Earth's atmosphere, nitrogen makes up about 78% of the air, while oxygen constitutes approximately 21%. The combination of these two gases is crucial for various biological and chemical processes on Earth.

Oxygen is essential for respiration in most living organisms, while nitrogen plays a significant role in maintaining the stability of the atmosphere and is inert in respiration for humans. Understanding the composition of air is fundamental for anyone involved in diving or using various gas mixtures, as it lays the groundwork for the study of breathing gases and their implications for decompression and gas management while diving.